The requirement for a surfactant where colloidal suspension or emulsions are employed, for example in the preparation of latexes, microspheres, or in suspending agents used as antipollutants, is well recognized in the art. Further, it is desirable to utilize a surfactant having the highest adsorption efficiency attainable. One example is the use of such material in a polymer latex used to obtain coatings which are impermeable to the passage of moisture and gases such as oxygen. In such systems, excess surfactant in the water phase of such latex, interferes with the impermeability characteristics of the latex by producing exudates at the coating surface. Further, the surfactant frequently interferes with adhesion of the latex to the substrate being protected or with cohesion of the coating to itself (heat seal). Still further, coatings containing excess surfactants have a high level of water leachables which oftentimes precludes the use of such materials in applications such as food wraps.
A further requirement for a successful surfactant for use in colloidal suspensions or emulsions is the ability of such material to remain on the surface of the disperse phase of the colloidal suspension or emulsion in the presence of other formulating agents or when the colloidal suspension or emulsion is diluted or concentrated. The structure of the surfactant is also important, i.e., whether such material lies flat along the disperse phase or is randomly attached to the surface of such disperse phase with a portion of its molecular structure extending into the continuous phase of the colloidal suspension or emulsion. It is the molecular structure of the surfactant and its method of attachment to the disperse phase of the colloidal suspension or emulsion which will determine the amount of surfactant required as well as the colloidal stability, viscosity and other rheological properties of the colloidal suspension or emulsion.
Prior known surfactant materials include the conventional nonpolymerizable water-soluble alkali soaps as described, by way of example, in U.S. Pat. No. 2,655,496. In general, these materials are characterized by relatively low energies of desorption and can easily be displaced or desorbed from a disperse phase in the presence of other materials having higher energies of adsorption or by dilution of the suspension or emulsion.
Other types of prior known surfactants having somewhat greater resistance to desorption are the surface active polymeric or polymerizable materials used for the preparation of latexes as disclosed, for example, in U.S. Pat. Nos. 3,177,172; 3,399,159 and 3,617,638; as well as the publication by Migranyan et al. (Vysokomolkulyarnye Soedineniya, Seriya B, 11, No. 8, 620-623, 1969). Basically, such prior art relates to the combination of monomeric materials formed into a polymer with an ionically substituted backbone to which is attached relatively long chain hydrophobic groups such as are present in the conventionally used soaps. yet another type of polymerized material, for used in latex preparation, are certain alkyl sulfide terminated oligomers as described by U.S. Pat. No. 3,498,943. These materials differ from the surfactants contemplated by the present invention in that they rely primarily on the hydrophobic thioalkyl end groups for adsorption into the disperse phase of the latex. Such materials are polymeric analogs of conventional soaps having a hydrophilic head and hydrophobic tail and are not representative of the present polyelectrolytes wherein the hydrophobic units are randomly distributed in the backbone of the polyelectrolyte and wherein such polyelectrolyte is adsorbed in the disperse phase of a dispersion in a substantially flat configuration which provides a high adsorption efficiency which, in turn, results in highly desirable properties in a variety of applications.